For the following table draw Gantt charts illustrating their execution using: a) Shortest job first scheduling, b) Shortest remaining time first scheduling, c) Priority Scheduling.... For the following table draw Gantt charts illustrating their execution using: a) Shortest job first scheduling, b) Shortest remaining time first scheduling, c) Priority Scheduling. Find Average waiting time, average response time, and average turn-around time for each case. Read more

Steps to Solve

1. Shortest Job First Scheduling

   In Shortest Job First (SJF), the process with the smallest execution burst time is scheduled first.

   • Calculate Gantt Chart:

     • At time 0, P0 arrives (burst = 7).
     • At time 2, P1 arrives (burst = 4).
     • At time 3, P2 arrives (burst = 5), but P0 executes first since it has the longest remaining time.
     • Continue scheduling:
     • Execute P1 next (P1, 2-6).
     • Then, execute P2 (P2, 6-11).
     • Finally, execute P3 (P3, 11-14).

   • Gantt Chart:

   | P0 | P1 | P3 | P2 |
   0    2   6   11   14
   

   • Calculate Times:
     • Turnaround Time (TAT) = Finish Time - Arrival Time
     • Waiting Time (WT) = TAT - Burst Time
     • Response Time (RT) = Time of first response.

2. Shortest Remaining Time First Scheduling

   In Shortest Remaining Time First (SRTF), the process with the shortest remaining time is executed next.

   • Calculate Gantt Chart:

     • P0 executes until time 2, then P1 arrives and has a shorter burst.
     • Continue evaluating the remaining times:
     • Execute P1 (2-6), P3 (6-9), then P0 (9-14), and lastly P2 (3).

   • Gantt Chart:

   | P0 | P1 | P3 | P2 |
   0    2   6   11   14
   

   • Calculate Times:
     • Employ the same time calculations as in SJF.

3. Priority Scheduling

   In Priority Scheduling, the process with the highest priority (lowest number) is executed first.

   • Calculate Gantt Chart:

     • At time 0, execute P2 (highest priority).
     • At time 3, P1 (next highest priority).
     • At time 6, execute P3.
     • Finally, execute P0.

   • Gantt Chart:

   | P2 | P1 | P3 | P0 |
   0    3   6   9    14
   

   • Calculate Times:
     • Similar calculations for TAT, WT, and RT as done in previous methods.

4. Calculate Average Times

   • Average waiting time: $\text{Average WT} = \frac{\text{SUM of WT}}{\text{Total Processes}}$
   • Average response time: $\text{Average RT} = \frac{\text{SUM of RT}}{\text{Total Processes}}$
   • Average turn-around time: $\text{Average TAT} = \frac{\text{SUM of TAT}}{\text{Total Processes}}$

5. Draw Process State Diagram and Explain Context Switching

   A process state diagram includes states such as "Running," "Waiting," "Ready," and "Terminated."

   • Context Switching: This is the process of saving the state of a running process, so it can be resumed later, allowing multiple processes to share a single CPU.